A number, represented by said letter, expressing the ratio of the circumference of a perfect circle to its diameter. The value of π has been calculated to many millions of decimal places, to no readily apparent purpose: no perfect circles or spheres exist in nature, since matter is composed of atoms and therefore lumpy, not smooth. Nature herself sometimes takes to rounding off the more extreme decimals of numbers when they get sufficiently small, as Prof. Heisenberg has pointed out. However, the continued extension of π provides a harmless exercise of computer power which would otherwise be misused playing Quake or surfing pointless web sites.